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cell-block-9 writes "Today the last section of the old Edison DC power grid will be shut down in Manhattan. 'The last snip of Con Ed's direct current system will take place at 10 East 40th Street, near the Mid-Manhattan Library. That building, like the thousands of other direct current users that have been transitioned over the last several years, now has a converter installed on the premises that can take alternating electricity from the Con Ed power grid and adapt it on premises.' I guess Tesla finally won the argument."

Good to see Wikipedia hold up under the mad scramble of 10,000 Slashdotters

Shesh...they have real servers and it's only read-only activity. As they are using MySQL, it's likely all cached hits to boot. As long as they have the bandwidth, it's likely a trivial load. It's not like/. has the hitting power it did five or six years ago.

Just like most of us here on Slashdot don't know (without the assistance of a search engine) who won the 1982 Super Bowl. Different things matter to different people and most people have things to worry about rather than wondering who the proponents of power transport via AC were.

Most of us here on/. certainly know who Mr. Tesla is and what he pushed for and we should take pleasure in being in such distinct company...except for the trolls and turds.

Do you have transmission lines that are three blocks in diameter? Then it's more efficient to convert at the source. What? You don't? Then I guess converting at the point of use is more efficient. Transporting the 5V and 12V levels that most consumer electronics use internally would be insane over more than a few feet because of voltage drop [wikipedia.org].

It would be more efficient to transmit DC, if we are talking about the same voltages. AC is impeded by inductance as well as resistance, so in addition to the inefficiencies of converting, you also are better off transmitting DC if it is the same voltage.

The trick is, transmitting at higher voltages is more efficient than transmitting the same power at lower voltage. This is because to send the same power at low voltage, you must send more current, and more current means more energy wasted as heat from the resistance of the line. So voltages from the generator are stepped way up before being transmitted.

And the reason AC won out is that it is much, much cheaper and easier to step up AC voltage (you just need a transformer, which is nothing but a couple coils of wire around an iron core) than to step up DC voltages (which requires a boost converter, which at its heart is a giant transistor [big enough to survive the voltages and currents of a power plant in this case] and a huge inductor [big fat coil of wire] along with timing and firing circuits to control the action of the transistor).

Boost converters are expensive, but over a long enough run of transmission line the advantages of DC over AC do make up the difference (as I recall, the break-even point is about a 400 mile long line). So you do find some long distance transmission lines that are DC. I know there is one out here in Sylmar, California that runs up to Washington state somewhere.

The big issue I have with DC is that its a potential safety hazard. Unlike AC which you'll feel if you touch one of the wires, with DC you don't feel it unless you are grounded or touching both wires of the circuit. The problem is that when you're grounded is the worst time to just realize that you're holding a live wire.With AC, the biggest concern is that you get it through either the heart or the brain, in most cases if you just touch the live wire in your house, you're most likely just going to get a ti

actually no, that means 80+ years ago that was true but now a high voltage dc transmission system is in fact more efficient, uses less condutors, eliminates need for sychnonization between different systems. HVDC also preferred for undersea long distance transmission because of less capacitive losses.

DC is still far more of a pain to convert than AC at least if you want high efficiancy and high reliability. While HVDC is certainly more efficiant for very long or undersea transmission lines it would be extremely difficult to build a power distribution grid based on it.

No, your regular computer power supply does not provide hundred of amps - tens, tops, and that is for a really power hungry system on a 110VAC line. Switching power supplies prices scale up rapidly with increasing power output.I didn't say anything about the "power supply", I was talking about the Motherboard, which feeds electricity to that power hungry CPU, taking in the 5VDC at 20 Amps and convert it to 1.33 VDC at 60 amps per unit

Yes, DC wins when using cables with high capacitance and also between power grids of different frequency. About 5 mins walk from my house is the anchor point for the UK France cross-channel HVDC link. The converter station is at Sellinge, about 10 miles away, and can ship up to 2GW in either direction. However, due to higher capacity on the French side (they have more nuclear), I understand the UK are net consumers of energy.Although the UK and France both operate at a nominal 50Hz, it is normal for actual

DC doesn't require high voltages, a DC line at a given voltage is slightly more efficiant than an AC line of the same voltage.

DC has two main problems

1: it is a pain to voltage convert. Voltage conversion is pretty vital to our modern use of electricity, you don't want 11KV in your home but you don't want to be transmitting 240/415 three phase or worse 120/240 split phase any significant distance. You also want much lower voltages for loads of equipment.

For equipment power supplies it isn't so bad, they generally don't have particularlly high efficiancies anyway, they tend to run at fairly low power and they tend to be in a nice indoor environment but building a DC equivilent of a pole pig with similar efficiancy and reliability would get pretty expensive.

2: DC is a pain to switch, switches and breakers would have to be either much bigger or much more complex for a given DC voltage than for the same AC voltage (the zero crossings of AC tend to break arcs).

Pain to convert doesn't even begin to describe it. AC can be both stepped up and stepped down with transformers. What are transformers? Basically coils of wire. You can step up and step down voltages HUGE amounts with basically more wire. Stepping up and stepping down DC are two different processes. Stepping down is really inefficient and stepping up requires caps (and caps don't really scale to voltages that high well). Also, it's waaay easier to turn AC into DC than the other way around. You can pretty ea

It's true that AC is much easier to step up and down. However, DC isn't stepped the way you are thinking. There are switching DC-DC converters that can step DC up or down with high efficiencies and don't need any particularly large capacitors, as they use inductors. They are far more complex, expensive, and failure-prone than transformers for high power, and don't work at all beyond a few thousand volts or so, but they exist.

Or that he died broke and alone because people like Edison stole his ideas and robbed him blind. Tesla was a genius and could have done so much more for the world if only things weren't controlled by rich people with no vision further than how much money they can make, right away, off an idea. Tesla's failure is a perfect example of capitalism at work.

but the real overriding realization with democracy and capitalism is that however much you think they suck, and they do suck in many ways, they are still better than any other system we can think of and have tried

No. Capitalism is the best system available, but that doesn't make it fair. It is up to the people within the system to try to make it fair. That includes pointing out the problems with it. His criticism isn't meaningless, it's important.

The failures of democracy aren't democracy itself, but rather of the fact that our implementation of democracy is poor in that it doesn't actually give people the representation in government that they should have. Its too easy to get re-elected, its too hard to break into politics without vast amounts of cash and/or support from existing politicians, its too hard to remove someone who is doing a shitty job, its not nearly transparent enough, the

Democracy: people vote and the power and law are made directly (volatile)
Republic: people vote and representatives implement the power and law (slow change over time, more stable)

Too bad these aren't the real definitions. Look it up. Your definition of "democracy" is actually the definition of "direct democracy", while your definitino of "republic" is actually the definition of "indirect democracy" or "representative democracy". A republic can be a direct democracy, a representative democracy, or neithe

As for capitalism being fair (or not), my grandma always said, "If you dont work you dont eat."

That's a good argument against capitalism, where capital, if you have it, works for you. Start out with enough, and you can eat damn well on investments and compound interest without ever working.And on the opposite side of the scale, if you can't work, you don't eat either.

Personally, I think effort-driven communism ("How much you eat depends on your effort to contribute") is theoretically the best system, but c

Or that he died broke and alone because people like Edison stole his ideas... Tesla's failure is a perfect example of capitalism at work.

Much of the good ideas that really propel technology are that way. Capitalism rewards manipulative wheeler-dealers far more than creativity. It rewards those who can best exploit creative ideas, not make them.

And?That's pretty typical. Example: who do you think of as the inventor of the telephone? Most people would say Alexander Graham Bell. But one could equally credit Antonio Meucci, Johann Philipp Reis, and Elisha Gray. Meucci especially. He beat Bell to it by over 20 years. But he was an Italian immigrant, spoke only poor English, and was effectively broke.

Not at all. He died broke because he was as inept financially as he was brilliant scientifically. He tore up a contract that would probably have made him a billionaire because he didn't want to bankrupt Westinghouse. Capitalism has its faults but Tesla's financial state upon his death is not one of them.

That's not to say that Edison cheating Tesla out of tens of thousands of dollars was a good thing, but Tesla survived that and ultimately ended up working with George Westinghouse. You seem to forget that

Tesla died broke because he spent all his money trying to create a "wireless power distribution" that made no sense. If he had spent more time reading physics and less time building 100+ foot Tesla coils. Were some of his inventions stolen? Undoubtedly. But I think he has only himself to blame for losing all his money.

You do realise that he repeatedly succeeded in wirelessly distributing power. We've been wirelessly distributing power for over a century thanks to his discoveries, from powering a crystal radio from the airwaves to RFID chips. Rather, I'd suggest he was too busy writing the physics books to make much money from them.

wireless power transmission is possible but not at efficiancies that makes it usefull for anything more than extremely low power items (like your crystal radio). Teslas ideas of large scale wireless power distribution were a pipe dream.

Very true, and it's a crying shame. Tesla was one of the brightest men of his generation, and the number of inventions and research he left behind is beyond impressive [wikipedia.org]. That, and he had this crazy-scientist image thing going along aswell:)

Most people answer with a blank stare whenever in mention the work of Tesla. While Edison's contribution is undeniable, he was more of a salesman than a scientist.

While the majority of people don't know who Tesla [wikipedia.org] was or what he contributed [wikipedia.org] to the modern world, it's safe to say that most of the people here on/. are - at least - aware of him.

If I ever make it to Belgrade, I'm planning to check out the Nikola Tesla Museum [tesla-museum.org].:)

Do to all the anti-gravity devices, free energy machines, and death rays which the Lovecraftian writhing of Tesla's decaying mind gave birth to--and to all the countless nuts propagating them--I would like to paraphrase a widely-attributed quote:

In Chicago it's ComEd, for Commonwealth Edison. In New York, it's Con Ed for Consolidated Edison. I think Massachusetts used to have a ComEd, though not sure if that was the same company as in Chicago, it stood for Commonwealth Edison (but these days it's called NSTAR in Mass).

The advantages of AC are mostly in transportation from the power station to the consumer. Internally, electronics use mostly DC, I think (correct me if I'm wrong here). Batteries store and release DC current, a computer's power supply converts to DC, etc.

For short distances and for use within IC it's quite useful. The conversion from AC to DC at lower voltages for use within computers produces quite a bit of heat (hence the fan in your PSU, yes I realize that even DC from a higher voltage to DC at a lower voltage produces quite a bit of heat) and so you find that some data centers are moving to converting from AC to DC outside of the cases and transporting DC directly to the servers.

There was an article on/. about this a while back and perhaps somebody who'd like to be modded up a bit can post the link.

Yep, for ever expanding definitions of "short distances." High voltage high power DC silicon is getting better and cheaper, so we're already seeing a few long-haul DC lines where the reduced radiative losses and increased carrying ability of the cables makes it more efficient. On the other end, DC converters are becoming ubiquitous inside electronics. Google wants to standardize on only one voltage (12V) coming from your computer's PSU, and anything that wants another voltage just has its own converter.

A few, but not very many. The main one is that many power uses require DC in the end, so AC has to be rectified and filtered before it's used -- and in doing so, some power is lost. When/where you're using a lot of power in a relatively restricted area, that can make a meaningful difference. Automobiles, for one obvious example, mostly use 12V DC systems (nominally 12V -- really around 14V). Aircraft, for another example, mostly run on 48V DC (IIRC). Some data centers have also gone to having a single big power supply, and then piping DC around to the individual computers. I haven't measured it personally, but they claim this can cut power usage by around 30% in some cases.

Another difference is that getting shocked by DC tends to be slightly less dangerous than the same shock from AC. A 110V DC shock to bare (unbroken) skin is is quite mild feeling, where most people in the US have found (sometime or other) than 110V AC is fairly uncomfortable, though usually not particularly dangerous (i.e. for every person who dies of electrocution, an unknown but certainly large number of others are shocked with no real consequence beyond surprise and discomfort).

DC power has many advantages over AC. Lower peak voltages for the same power delivered. No reactive losses. You don't need to synchronize generators feeding the system.

AC power has one HUGE advantage and maybe other smaller ones. You can cheaply and easily step the voltage up and down. Stepping A DC voltage up and down is much more complex. DC to DC converters are getting cheaper and better to the point that people are proposing and building high voltage DC power distribution systems.

As related here [wikipedia.org] high-voltage DC transmission is more efficient than high voltage AC transmission for a number of reasons, and it has other benefits as well in allowing potentially unsynchronized AC systems to transfer power. The main problem is efficient voltage conversion, which requires more infrastructure than an AC system with equivalent power transfer capability.

Actually DC current is more efficient than AC in transmitting power due to there being no reactive component of the power. The main problem with DC is that it cannot be transformed to higher voltages which save a lot of energy losses. There is actually a very long DC transmission line to California that uses DC power. They convert to AC at the end of the line. AC is also a much safer means for transmitting power. It is nearly impossible to extinquish a fault on a DC line because the voltage never reaches a zero point. Protection devices on AC lines rely upon the zero point to extinquish faults.

How long until a significant proportion of local users have a hybrid AC/DC system to manage power distribution from power generated on site? Tesla certainly won the medium power, wide area power distribution battle, but there are a lot of developments taking place that will increase the visibility of DC power generation.

DC is actually used extensively in modern power grids, the main advantage being that there is no need to synchronize the phase from different generating stations or subgrids. For example, the Pacific Intertie [wikipedia.org] transmits three gigawatts of direct current between Los Angeles and eastern Washington state. (Power is sent from LA to Washington in the winter, covering the demand of electric heating in the pacific northwest; and from Washington to LA in the summer to power our air conditioners.)

Some people disagree with the Slashdot system that "funny" mods don't contribute to karma. So some people choose a different positive mod to use when something's funny.

I tend to agree. If I find something worthy of using a mod point for any reason, then I think it should be reflected in that user's karma. Why discriminate against humor?

Because most of the "funny" posts aren't very funny at all (i.e. the quality of "funny" moderations is lower than the quality of other moderations)?

Because Slashdot is intended to generate informative and insightful discussion rather than humor?

Deliberately using the wrong category when moderating reduces the readers ability to filter the posts in the way that they want. Moderators are supposed to categorize posts. They are not supposed to care about the karma of the authors.

The inventor Nikola Tesla spent the last ten years of his life in near-seclusion in Suite 3327 (where he also died), largely devoting his time to feeding pigeons while occasionally meeting dignitaries.

When I lived in Cambridge, I sometimes visited friends in Boston who had 600VDC elevators using power from the city.Later elevators still used 600VDC but used a dynamotor; that whine you used to hear when you pressed an elevator button elsewhere was the dynamotor starting, to convert to 600VDC from the 120VAC line current. Eventually, elevator manufacturers stopped using it, but when you hear that whine in a medium-old elevator, you know what is is.

What you're hearing is not a dynamotor, but something called a Ward Leonard drive. It's a fixed-speed motor driving a generator, but its purpose is speed control. The field current of the generator, which is small, is adjusted to control the larger output of the generator. The variable output of the generator then drives the elevator motor. The Ward Leonard drive is thus a big power amplifier. Until power semiconductors got big enough, which wasn't really until the 1980s, this was the most effective way to smoothly speed-control large motors.

A dynamotor has a common field for the input and output sides, but a Ward Leonard drive does not.

The reason the subways use DC was that at the time the subways were developed, DC motors were smaller, lighter, cheaper and more efficient than variable speed AC motors. AC series motors were developed for railway service (e.g. the New Haven electrification between NYC and New Haven), but those required lower frequency (typically 25 Hz in the US, one exception was the Visalia Electric at 15 Hz and 16 2/3Hz in Europe). Commercial frequency electrification didn't become practical until the 1950's with the development of ignitron and silicon rectifiers.

AC's advantage of high voltage transmission doesn't apply to subways as 1200V seems to be the limit for third rail. 2400VDC was tried in 1915 on the Michigan Railways (an electric interurban in central Michigan) with abysmal results - the voltage was changed to 1200V within a year of the initial installation.

I would assume it wasn't better because in most cases electricity has to travel over a long distance UNUSED between production and final usage point (ie: power generator and someone's home). AC can relatively easily be upped to high voltage which is good for sending over long distance (much higher efficiency) IF you don't need to use it along the way. Also I think single speed AC motors are easy to make.Subways (and the like) are unique because the transmission line is also your final output/usage point. Yo

First of all, let me tell you that Tesla is one of my role models. He is one of the reasons I studied electrical engineering - with a passion. And AC, if you want, is the "winner" for all intents and purposes. The future really validated Tesla's AC system. There have been other folks that helped the adoption of the AC system, like Proteus, another role model for me.

Said all that however, high-voltage DC, a transport technology that starts to make sense nowadays, thanks to high-power solid-state switching elements, has many advantages over AC in terms of losses and cable utilization. You can transport more energy via DC than AC, across the same thickness cable. And you have practically no losses due to parasitic capacitances and inductances. The corona effect is much easier to control, too.

So, if I was forced at gunpoint to make a prediction for the electricity transportation in 150 years from now, I'd say hihg-voltage DC.

So what you need to achieve is high voltage. But in the past, that wasn't possible with DC, because there was no _efficient_ way to transform the voltage/current aspect of the power line for DC, only for AC.

Kinda sad to me but it was in the way of progress. Lots and lots of buildings still use the old DC elevators here in New York City. Just yesterday I loaded in to Bayard's in downtown Manhattan into a 4x4 foot elevator that I swear Otis himself must have installed. I love how you have to hold the lever to go up and down and manually align the elevator to the floor. The elevator lights are powered by the DC current as well. At Pratt Institute they used to have those old DC elevators that were powered by an ancient motor generator set that was dated back to the 30's. Hell up until 1999 the MTA still had an old DC substation that had Rotary converters for the subway. ConEd also kept the 25 cycle plants running to feed those substations until the early 90's.

If you want a feel of old DC equipment from the days when if you wanted power you had to make your own, head down to Pratt Institute (located in Brooklyn on Willoughby ave. and Hall st.). They still have 3 steam driven reciprocating piston dynamos built by Ames Iron Works. They work but are only for show. And to top it off they also have a steam turbine dynamo all of which is hooked to a large open marble panel board with knife switches, carbon arc circuit breakers and blade fuses. The panel is still live on the AC side. The Motor generator I mentioned is still there. You can go down to the Pratt engine room and get a tour from Conrad Milster, the Chief engineer who keeps the place running. The large 1930's brick steam boiler still heats the campus and the surrounding neighborhood. The site is an IEEE land mark and walking down there is like going back in time, a real treat.

This should give you a pretty good idea of the state of NYC's infrastructure.It's been pushed to its absolute limits in terms of age and longevity. The subways have served us well, but it's only been in the last few years that we've stopped neglecting them, and replacing outdated/dangerous systems with more efficient modern counterparts. (There was also the issue that the only people who knew how to service some of the archaic equipment that the MTA was running had been dead for at least 20 years)

It keeps being repeated, even in this article which says "it can be transmitted long distances far more economically than direct current", that AC is more efficient. This is not really true. The advantage (and pretty much the only advantage) that AC has over DC is that it is relatively simple to change voltages.

Over the short-haul, this is good since losses are primarily resistive and losses are related to the amount of current flowing in the conductors. Power in my neighborhood is delivered at 12,000V and down-converted to 120/240 by transformers located every few houses. Delivering power at 120V would require 100 times the current and massively larger conductors. Once it gets to my house, with the exception of some motors and some lights, everything from TV to stereo to computer ends up having to take that power and reconvert it to DC.

But AC has far higher losses through capacitance and inductance which become severe over long distances. This is why some current and other planned long-haul transmission routes use DC. A good example of this is the 800-kilovolt DC line that connects into the Sylmar Terminal Station near Los Angeles.

Apparently, the use of Extra High Voltage DC is being proposed for a number of new long-haul transmission systems and it is the high losses incurred by AC over long distances that is driving the use of DC.

What sort of electric devices even come with DC input? Most everything has a AC/DC converter built into it. Does that mean that every electronic device on the premises needs both a DC/AC converter and a AC/DC converter chained together? Wow...

I think the most beautiful piece of old AC to DC conversion technology was the mercury arc rectifier...apparently these devices were still used on some branches of the NYC subway until late in the 20th century. A video of one in operation can be seen at http://www.youtube.com/watch?v=Rt-a8fxgtno [youtube.com]

A center-tapped transformer was connected to two anodes to form a full-wave rectifier(some had more anodes and were used for 3 phase power), and a pool of liquid mercury was used as the cathode material which would form an arc only if the anode was positive. A keep-alive electrode kept the interior full of vaporized mercury to facilitate the discharge. I'd sure like to have my own. Unfortunately an average sized mercury arc rectifier contains around 2 pounds of liquid mercury, so if it ever broke, my neighborhood would have to be decontaminated, my home razed to the ground, and the rubble buried in a concrete encasement.

Uhm, no, everything is *not* technically DC. Yes, anything that uses electronic controls or is electronics will have either an internal transformer/rectifier or an external wall-wart, but lots of things use AC directly. Motors in power tools, dishwashers, refrigerators, vacuum cleaners, and most power electric appliances (not to mention modern elevators) are AC motors. Incandescent *and* flourescent lighting is a direct AC user (but LED's use DC, of course). Fans (not the PC kind), blowers, electric lawnmowers, even electric heat, all use AC directly.